Polymer-matrix composites offer unique combinations of properties and are useful in a wide range of applications. Such composites may be fabricated utilizing either thermosetting or thermoplastic polymer matrix materials with a variety of particulate or fibrous fillers or reinforcements. It is generally advantageous to have strong adhesion between the polymer matrix material and the surfaces of the various particulate or fibrous substrates and there is considerable art related to substrate finishes and other treatments to optimize adhesion to polymer matrices. For example, in the production of long-fiber reinforced composites, improved adhesion between the polymer matrix and the fiber reinforcement leads to increased material performance. Good adhesion is particularly important where failures are likely to occur by delamination or by other adhesive failure modes.
As described in, for example, U.S. Pat. Nos. 5,840,238, 6,310,121, and 6,525,125, the disclosures of each of which are incorporated herein by reference, polymers generated by olefin metathesis processes are attractive as composite matrix materials. Of particularly beneficial use are the polymers generated by the ROMP of cyclic olefins. The low viscosity of cyclic olefin resin formulations and the ability to control ROMP kinetics (e.g., U.S. Pat. Nos. 4,708,969 and 5,939,504, the disclosures of both of which are incorporated herein by reference) facilitate composite processing and manufacture, and the corrosion resistance and high toughness of ROMP polymers leads to good composite durability. Additionally, certain properties of ROMP polymers, e.g., mechanical strength and stiffness, heat distortion temperature and solvent resistance, can be further enhanced by crosslinking induced via thermal treatment (e.g., U.S. Pat. No. 4,902,560, the disclosure of which is incorporated herein by reference) or chemically by addition of peroxides (e.g., U.S. Pat. No. 5,728,785, the disclosure of which is incorporated herein by reference).
Commercially important ROMP resin formulations are generally based on readily available and inexpensive cyclic olefins such as dicyclopentadiene (DCPD), norbornenes, cyclooctadiene (COD), and various cycloalkenes. However, in contrast to traditional resin systems (e.g., epoxy, acrylate, urethane, and polyester resins) based on polar functional group chemistries, these nonpolar ROMP resins have poor intrinsic adhesion to the relatively polar surfaces of common carbon, glass, or mineral fillers and reinforcements. The addition of various silanes to such resin formulations for improvement of electrical and mechanical properties of ROMP polymers is described in U.S. Pat. Nos. 5,840,238, 6,001,909, and 7,339,006, the disclosures of each of which are incorporated herein by reference. Many widely used commercial silanes do not give optimal properties with ROMP polymers, however, and the greatest enhancements are only obtained when the silanes comprise groups with high metathesis activity (the relative reactivity of various metathesis active groups is described in J. Am. Chem. Soc., 2003, 125, 11360-11370).
As described in International Patent Application Number PCT/US12/42850, the disclosure of which is incorporated herein by reference, it was discovered that the addition of an adhesion promoter comprising a compound containing at least two isocyanate groups provides beneficial improvements in the adhesion of an olefin metathesis (e.g., ROMP) composition to substrate materials, such as, for example carbon and glass reinforcement materials. According to International Patent Application Number PCT/US12/42850, use of an adhesion promoter comprising a compound containing at least two isocyanate groups provided improved adhesion of ROMP polymer matrices compared to ROMP polymer matrices without such adhesion promoters, where adhesion of ROMP polymer matrices to substrate materials was measured by the short beam shear method according to ASTM D2344. Interlaminar shear strength (ILSS) is a measure of the adhesion and/or compatibility between the polymer matrix and the substrate material in a composite.
While International Patent Application Number PCT/US12/42850 demonstrated that compounds containing at least two isocyanate groups are effective to improve the adhesion of ROMP polymer matrices to substrate materials (e.g., carbon and/or glass reinforcement materials), the issue of making ROMP polymer-matrix composites possessing strong adhesion between the polymer matrix and substrate material as well as having improved impact properties (e.g., improved impact strength or improved impact toughness) was not specifically addressed.
It is known in the art that the impact properties (e.g., impact toughness or impact strength) of ROMP polymers can be improved by the use of impact modifiers. Typical impact modifiers known in the art for use with ROMP polymers include natural rubber, butyl rubber, polyisoprene, polybutadiene, polyisobutylene, ethylene-propylene copolymer, styrene-butadiene-styrene triblock rubber, random styrene-butadiene rubber, styrene-isoprene-styrene triblock rubber, styrene-ethylene/butylene-styrene copolymer, hydrogenated styrene-ethylene/butylene copolymer, styrene-ethylene/propylene-styrene copolymer, ethylene-propylene-diene terpolymers, ethylene-vinyl acetate, and nitrile rubbers. Specific impact modifiers known in the art include polybutadiene Diene 55AC 10 (Firestone), polybutadiene Diene® 55AM5 (Firestone), EPDM Royalene® 301T, EPDM Buna T9650 (Bayer), hydrogenated styrene-ethylene/butylene-styrene copolymer Kraton® G1651H (Kraton Polymers U.S. LLC), Polysar® Butyl 301 (Bayer), hydrogenated styrene-ethylene/butylene-styrene copolymer Kraton G1726M, Engage™ 8150 ethylene-octene copolymer (DuPont-Dow), styrene-butadiene Kraton D1184, EPDM Nordel® 1070 (DuPont-Dow), polyisobutylene Vistanex® MML-140 (Exxon), hydrogenated styrene-ethylene/butylene-styrene copolymer Kraton G1650M, hydrogenated styrene-ethylene/butylene-styrene copolymer Kraton G1657M, and styrene-butadiene block copolymer Kraton D1101. For example, U.S. Pat. Nos. 4,520,181, 4,943,621, and 6,838,486 disclose the use of impact modifiers to improve the impact properties (e.g., impact toughness or impact strength) of ROMP polymers, where one or more impact modifiers are typically dissolved in a cyclic olefin resin and the selected impact modifier(s) should not interfere with the polymerization reaction. Therefore, when making ROMP polymer-matrix composites having enhanced impact properties (e.g., improved impact toughness or impact strength) it is important that the impact modifier does not interfere with the polymerization reaction and it is also important that the impact modifier does not interfere with the ability of an adhesion promoter to effectuate adhesion between the ROMP polymer-matrix and the substrate material (e.g., glass and/or carbon reinforcement material).
Surprisingly, the inventors have discovered that hydrogenated styrene-ethylene/butylene-styrene copolymers known in the art for use with ROMP polymers as impact modifiers may interfere with the ability of adhesion promoters comprising at least two isocyanate groups to effectuate adhesion between ROMP polymer-matrices and composite substrate materials thereby adversely affecting the mechanical properties of the polymerized resin and/or polymer-matrix composite.
Despite the advances achieved in the art, particularly in the properties of olefin metathesis polymers (e.g., ROMP polymers) and their associated applications, a continuing need therefore exists for further improvement in a number of areas, including the manufacture of polymer-matrix composites, in particular ROMP polymer-matrix composites, where such composites possess strong adhesion between the polymer matrix and substrate material (e.g., carbon and/or glass reinforcement materials) as well as enhanced impact properties (e.g., improved impact strength or impact toughness).